I think speed deadlifts would be more beneficial only because you're training your CNS with the actual lift since my goal is to speed past my sticking point about 1/3 of the way up. As for power, I'm bad at math, but I personally cannot compare pulling a heavy deadlift for a single as fast/hard as I can vs. trying to be more technical with a clean. That's pretty much all I was saying..
I just went to midwestbarbell to get an idea about this (as I usually do). I see some people doing cleans to kick off their ME Deadlift up to a certain weight albeit 225-315, then working up to a 1 RM for the conventional deadlift. This is something I'm going to try out tomorrow during my ME day since I have wide parallel as my max squat, and conventional deads as my max dead.
At least this way I can practice this lift while having it act as a perfect warmup for my deadlifting. Of course I'm not going nowhere near balls to the wall with these, but it will give me some extra volume which I find most beneficial for all around strength for me..